Frequently used in sea and lake to study fish populations, the use of hydroacoustic methods in shallow waters is increasing. The number of fish passing through Beaucaire-Vallabregues lock, first obstacle on the river Rhone, is estimated using a SIMRAD EY500 split-beam sounder, frequency 70 kHz. Two transducers sample about 35 % of the lock's section. For each lock cycle, the number of fish going across the lock is indicated. The characteristics of the fish crossing (dates, position, time and delay) are shown. Current analyses do not permit to discriminate the two main species which cross the lock, the shad (Alosa fallax) and the mullet (Mugil cephalus).

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